Existing personal computers offer multiple external peripheral interfaces for attaching multiple peripheral devices to a host computer. An Apple Computer, Inc. Macintosh personal computer, for example, typically has (i) an Apple Desktop Bus interface for a keyboard and a mouse, (ii) a Small Computer System Interface (SCSI) for disk drives, and (iii) an RS-232/RS-422 interface for a printer and a modem. All three interfaces are necessary for the Macintosh personal computer because not any one of these standard interfaces can accommodate all the peripheral devices.
On a small, hand-held portable computer such as a so-called "PalmTop computer" or "Personal Communicator", however, providing several different external peripheral interfaces presents a number of problems. From a user's perspective, it is confusing to employ multiple different interfaces, each having its own protocol and connector. Further, there may not be an adequate amount of physical space on the PalmTop computer to provide numerous connectors and the power requirements of separate standard peripheral interfaces are onerous for battery powered hand-held computers. In addition, the cost of supporting multiple different external interface standards in terms of number of logic gates and number of connector terminals is significant when manufacturing for the consumer computer market.
Even if a host PalmTop computer were to use only one of the above standard interfaces to accommodate a limited set of peripheral devices, and even if this standard interface was redefined to require less power, such a conventional interface would either be low performance, e.g., the Apple Desktop Bus runs at about 10 KBits/second, or complex to use, e.g., SCSI requires configuring peripherals, attaching special terminators, and shutting down the computer for reconfiguration.
Alternatively, a new external interface standard called IEEE P1394 could be used. Although this new interface standard potentially satisfies some of the performance and ease-of-use requirements of a PalmTop computer peripheral interface, the interface nevertheless requires additional complex, non-standard, interface circuitry to the peripherals. Such complex interface circuitry would make it difficult for small, low volume peripheral manufacturers to make simple peripheral devices at low cost. Moreover, employing IEEE P1394 would also require the PalmTop host computer to incorporate an expensive support chip having approximately 20,000 gates.
Accordingly, a single, low power, easy-to-use, high performance, serial bus suitable for use on a hand-held PalmTop host computer with a wide variety of peripheral devices is needed.